The invention relates to the manufacture and recovery of alkali-metal tetraorganylborates, such as sodium tetraphenylborate. Specifically, the invention makes use of a solvent pair including a complexing agent (tetrahydrofuran) and an aromatic comPound (toluene) which facilitates the recovery of the alkali-metal tetraorganylborate.
Tetraorganylborate compounds are useful for binding with specific radioactive material, i.e. cesium-137, and can be used to separate radioactive material from its carrier mass, therefore reducing significantly the amount of radioactive bulk. In practice, one use for tetraorganylborate compounds is to greatly reduce the mass and volume of radioactive wastes in, for example, disposal applications. The process can also be used for making other alkali metel tetraakyl- or tetraarylborates, trialkyl- or triarylborates, and alkyl and aryl Grignards.
Prior art methods for manufacturing alkali-metal tetraorganylborates typically use solvents consisting of 100% tetrahydrofuran (THF) or diethyl ether. Most prior art processes also require the use of waste evaporators, because of inefficient water economy, and those prior art processes using 100% THF as the solvent typically require two distillation columns to operate in order to break the tetrahydrofuran (THF) and water azeotrope. The lack of aqueous waste treatment by liquid/liquid extraction usually results in high product losses. Such prior art systems also exhibit less efficient raw material usage and are unable to recycle brine effectively without creating secondary wastes. Also, the prior art systems typically yield a product with a much lower purity, and the product must be recovered directly from a solvent stream.
U.S. Pat. No. 3,405,179 discloses a process for producing a triarylborane by reacting an aryl Grignard reagent with boron trifluoride. An inert hydrocarbon solvent is also disclosed. Inert hydrocarbon solvent systems without ethers present for preparation of Grignard reagents are known but are typically hard to initiate, give low yields and the product tends to precipitate which makes it difficult to handle. In contrast, the process of the present invention initiates easily, yields virtually all of the alkali-metal tetraorganylborate produced in the manufacturing step, and yields this product in an aqueous raffinate.
U.S. Pat. No. 3,475,496 teaches the use of Grignard reagents with boron trifluoride. A triarylborane is produced through the concurrent or simultaneous formation of a Grignard reagent and its reaction with a boron compound. The process of the present invention requires the use of a three reactor sequences which make possible dedicated usage for and recovery of each intermediate product in the alkali-metal tetraorganylborate manufacturing step. Thus, reactor 112 of the present invention is used solely for Grignard production and a heel is left after each run to provide activated magnesium to allow immediate re-initiation of the next Grignard. Reactors 112 and 122 of the present invention are kept dry at all times and do not have to be cleaned of water and solids each cycle.
U.S. Pat. No. 4,510,327 relates to the preparation of alkali-metal tetraorganylborate compounds by reacting triorganylboranes with alkali-metal hydroxide or alkoxide compounds. Solvents may be used, but are not required. In this process it is necessary to first prepare triorganylboranes which usually are not available commercially and are difficult to be converted to useful forms. Alkali-metal tetraorganylborates are produced and recovered by the process of the present invention in a novel process different from the above, which, as a consequence, avoids the above process difficulties.
European Patent No. 0,153,885 discloses specific tetraarylborate-ammonium complexes and their uses as antifouling, antiseptic, and antifungal agents. The European patent uses boron trifluoride diethyl etherate as the boron source, and toluene, used solely as a potential solvent component for separating the organic layer from the aqueous layer for product isolation. Furthermore, in the European patent, during the product isolation step the solvent is simply stripped down, leaving many impurities in the process. The disadvantage inherent in this patent is the use of liquid liquid extraction techniques; therefore, only alkali metal tetraorganylboron compounds in the aqueous phase may be extracted, leaving behind impurities in the organic layer.